Analysis of the nitriding process during the heat treatment of the inner ring gear by the high-frequency induction annealing machine

The inner ring gear is an inner ring gear in the end drive of a wheeled tractor. It is an important part of the planetary reducer of a wheeled tractor. The module is 4.25 and the number of teeth is 70. During the heat treatment process using a high-frequency induction annealing machine, it usually requires Using 42CrMo steel for nitriding treatment, the tooth surface nitriding layer depth is required to be ≥0.1mm, the tooth surface hardness is ≥600HV, and the core hardness is 24~35HRC. The quenching and tempering hardness of the inner ring gear matrix is appropriately controlled within the upper limit, generally limited to 28 to 35HRC, to increase the strength of the matrix. The working conditions of wheeled tractors are relatively harsh. Because the planetary reducer is a key component, it plays the functions of speed reduction, power transmission, etc., and has high reliability requirements. During acceptance, 1000 hours of full load operation and 2000 full load impact tests are required, and it must not fail.

Nitriding treatment refers to a chemical heat treatment process that allows nitrogen atoms to penetrate into the surface of the workpiece in a certain medium at a certain temperature. Nitrided products have excellent wear resistance, fatigue resistance, corrosion resistance and high temperature resistance.

Nitriding treatment is a very effective way to improve the gear contact fatigue life when using a high-frequency induction annealing machine to heat treat the inner ring gear. The improvement of the fatigue limit mainly lies in the favorable residual internal stress formed in the nitriding layer. The higher the nitrogen concentration absorbed in the nitriding layer, the greater the volume change of the nitriding layer, the greater the compressive stress in the nitriding layer, the higher the matrix strength, the stronger the effect of hindering the expansion of the nitriding layer, and the greater the compressive stress in the nitriding layer. big. If the strength of the matrix increases, the plastic deformation resistance of the gear teeth also increases, which is beneficial to preventing the occurrence of contact fatigue. The depth of the nitriding layer is controlled between 0.35 and 0.55mm. The lower limit depth only slightly exceeds the distribution depth of the maximum shear stress. Considering the inevitable sliding friction on the tooth surface, the shear stress peak will only move outward. Due to the good effect of residual compressive stress, the peak value will be reduced, and there is no need to consider more safety factors. The upper limit is no longer much higher. In addition to considering a certain range to facilitate operation and saving nitriding time as much as possible, the main consideration is that a greater increase in the depth of the nitrided layer will reduce the surface residual compressive stress and bring adverse effects. The surface hardness should be ≥550HV .